1. Field of the Invention
The present invention is directed to a presentation device for presenting a volume dataset with a number of volume data elements as a perspective, two-dimensional image rotatable around a basic rotational axis.
2. Description of the Prior Art
Devices of the above type are known which have a data memory for storing the volume dataset, a computer unit for determining the image from the volume data elements of the volume dataset, a display unit, for example a monitor, at least for the presentation of the image and at least one input means, for example a keyboard and/or a mouse control. In such devices, a position in the volume and a data value are allocated to each volume data element. A perspective, two-dimensional image covering a spatial angle is determined on the basis of the volume data elements, a point of vision and an optical axis containing the point of vision, and is presented via the display unit. The point of vision is displaceable along the optical axis on the basis of interactive inputs. The point of vision and, with it, the spatial angle that is covered are rotatable around a basic rotational axis on the basis of interactive inputs. The basic rotational axis intersects the optical axis at a basic intersection angle in a pivot point.
Such presentation devices are employed in medical fields for the presentation of tomograms or other three-dimensional reconstructions of patient images, for example in X-ray angiography. The above-described manner of employment is referred to as manual fly.
When the volume data elements represent a portion of a vessel system, for example a blood vessel system, the point of vision is placed in the inside of a vessel in the manual fly. The medical practitioner can then implement virtual endoscopy with the manual fly.
In the known devices, the basic rotational axis lies at a fixed distance from the point of vision. The requires a very dexterous interactive input on the part of the medical practitioner in order to alternately shift the point of vision along the optical axis and rotate the image and the point of vision around the basic rotational axis in common. If the medical practitioner is not very experienced or dexterous, he/she can only advance very slowly and laboriously in the vessel system. In the extreme case, there is even the risk that he/she willxe2x80x94virtuallyxe2x80x94puncture the vessel wall, no longer find the way back into the vessel system and must begin the virtual endoscopy anew. In practice, this has in minimal use of the manual fly option in presentation devices that offer the manual fly mode.
U.S. Pat. No. 5,555,366 discloses a computer graphics system for the selective model formation of molecules and researching chemical and physical properties. The two-dimensional and three-dimensional presentations of the molecules can be modified with the editing tools of the system, whereby the modifications are transferred into the other presentation.
U.S. Pat. No. 5,891,030 discloses a device that reproduces tubular structures of a human body, for example the gastrointestinal tract, with the assistance of a CT scanner with a work station. The center line of the large intestine is thereby identified. The work station compiles CT data such that axial tomograms, transluminal cross-sectional images and intraluminal volume rendering images are shown.
An object of the present invention is to provide a presentation device wherein a manual fly within a vessel system is enabled in a simple way so acceptance by the users, particularly medical practitioners, is thus improved.
The object is achieved in a presentation device wherein volume data elements within the spatial angle that is covered are selectable, and wherein the pivot point is defined dependent on the data values of the selected volume data elements.
As a result, the basic rotational axis can be positioned in a simple way so that it always lies within the vessel system. An inadvertent departure from the vessel system is no longer possible.
When the selected volume data elements lie on the optical axis or in the proximity thereof, the determination of the pivot point can ensue especially quickly. Generally, the data values of the volume data elements contain at least one transmission coefficient. It is therefore possible to determine an overall transmission from the point of vision to the respective, selected volume data element for the selected volume data elements, and to define the pivot point dependent on the overall transmission.
The evaluation can, for example, ensue so that those volume data elements are determined from the selected volume data elements for which the overall transmission exceeds or falls below a transmission limit. A terminal volume data element that lies closes to the point of vision is determined from these volume data elements, and the pivot point is defined on the basis of the terminal volume data element.
Alternatively, it is possible for the selected volume data elements to be checked for a truncate condition independently of one another, and a terminal volume data element that lies closest to the point of vision is determined from the selected volume data elements meeting the truncate condition. The pivot point is determined on the basis of the terminal volume data element. The truncate condition can, for example, be that the data value of the volume data element lies within a prescribable value range, for example between a lower barrier and an upper barrier.
The pivot point need not necessarily coincide with the position of the terminal volume data element but can be spaced therefrom by a distance.
When the pivot point lies between the terminal volume data element and the point of vision, the rotational axis in the manual fly always lies within the virtually endoscoped vessel.
In an embodiment wherein the spatial angle can be varied by interactive inputs, a more flexible manipulation of the presentation device is achieved.
When the pivot point is determined after every displacement of the point of vision, the user can divide a rotation into a number of partial rotations upon retention of the pivot point.
When the optical axis is laterally displaceable and the pivot point is also determined after every displacement of the optical axis, an even more flexible manipulation of the presentation device is achieved.